An electric power steering device which gives steering assist power to a steering mechanism of a vehicle has conventionally been an electric motor driven according to the steering torque applied to a handle (steering wheel) by a driver. Although a brush motor has conventionally been widely used as an electric motor of an electric power steering device, a brushless motor has recently been also used from viewpoints of improvements in reliability and durability, reduction of inertia, or the like.
In order to control the torque generated in a motor, generally, a motor control device detects an electric current which flows into the motor, and performs PI control (proportional integral control) based on the difference between an electric current to be supplied to the motor, and the detected current. In order to detect currents of two or more phases, two or three current sensors are provided in the motor control device which drives a 3-phase brushless motor.
In addition, in connection with the present application invention, obtaining a d-axis voltage instruction value and a q-axis voltage instruction value using the circuit equation of a motor is disclosed in JP-A-2001-187578. Additionally, correcting a d-axis current instruction value according to the temperature of a motor is disclosed in JP-A-2000-184773.